It is not easy to make repeatable and accurate measurements in analytical systems such as consumer devices using an electrochemical cell. Many constraints contribute to the difficulty of this task. The consumer device must be light in weight, small and reliable. The price cannot be too high. The device may be running on a new battery or an old one, and the user cannot be relied upon to perform manual calibration steps. The repeatability and accuracy of the measurements must be preserved even in the face of temperature changes and user decisions such as whether or not to use a display backlight.